1. Field of the Invention
The present invention relates to a composition for hard coat, and an article having a hard coat layer and a method for producing the article. More specifically, the present invention relates to a composition for hard coat capable of forming a satisfactory hard coat layer in various articles required to have properties such as anti-staining property, anti-staining durability, scratch resistance, abrasion resistance and antistatic property, an article having, on the surface thereof, a hard coat layer having these various properties, and a method for producing the article.
In particular, the present invention relates to a composition for hard coat capable of forming a hard coat layer having anti-staining property, anti-staining durability, scratch resistance, abrasion resistance and antistatic property, on the surface of each of the following, without deteriorating the optical property and the recording properties: information recording media; optical lenses; optical filters; anti-reflective films; various display elements such as liquid crystal displays, CRT displays, plasma displays and EL displays; and the like, and relates to a method for forming a hard coat layer and a product having a hard coat layer formed thereon.
2. Disclosure of the Related Art
In these years, there have been used as information recording media a various types of information recording media such as CD, MD, MO, DVD, BD (Blu-ray Disc), and HD-DVD. Among these information recording media, CD, DVD, BD and HD-DVD are so-called bare discs not inserted into cartridges. These bare discs tend to undergo stain or fingerprint adhesion on the signal recording/reading side surface, and there occurs a possibility that such stains cause troubles at the time of recording/reproducing. These bare discs have a problem that scratches and the like tend to be formed on the signal recording/reading side surface also at the time of insertion/removal of the disc. Accordingly, these bare discs are generally improved in properties such as anti-staining property, scratch resistance and abrasion resistance by providing a protective film and/or a hard coat layer on the signal recording/reading side surface.
In particular, information recording media such as BD and HD-DVD said to be next-generation DVD are undergoing promoted miniaturization of recording pits, and are characterized by undergoing high-density recording. For example, the laser spot size of BD is extremely as small as about ⅕ the spot size of conventional DVD. Accordingly, information recording media such as BD and HD-DVD may suffer from a crucial failure in recording and/or reproduction, caused by such minute scratches or stains on the recording side surface of the discs that cause no troubles in conventional CD, DVD and the like. Therefore, it is strongly demanded to provide, on the surface of the information recording media, a hard coat layer excellent in anti-staining property and abrasion resistance such that no fingerprint is adhered on the surface of an information recording medium, or even if fingerprint is adhered on the surface of an information recording medium the fingerprint can be readily wiped off without damaging the surface.
Among the above-described information recording media, the media used as bare discs have an additional problem that dust adhered to the disc surface also significantly affects the recording and/or reproduction. Therefore, such information recording media are strongly demanded to be excellent in antistatic property as well as the anti-staining property, scratch resistance and abrasion resistance.
Also, in articles other than the above-described information recording media, for example, optical lenses, optical filters, anti-reflective films and various display elements such as liquid crystal displays, plasma displays and EL displays, or the like, it is strongly demanded to provide, on the surface of these articles, a hard coat layer excellent in anti-staining property and abrasion resistance such that no fingerprint is adhered on the surface of such articles, or even if fingerprint is adhered on the surface of such articles the fingerprint can be readily wiped off without damaging the surface. These various display elements are further required to have antistatic property in order to prevent the adhesion of dust, oil mist (dust mixed with oil and fat) in the air or the like, and to prevent the generation of electric signal noises due to the static electrification of the display elements.
As a method of improving the anti-staining property of a hard coat layer, there has been proposed a method of improving the anti-staining property (water repellency and oil repellency) of the surface of an article by applying silicone oil or a fluoropolymer to the surface of the hard coat layer. However, in this method, the hard coat layer is formed by applying an anti-staining agent onto the surface of the article, and hence this method offers a drawback that the anti-staining agent is dissipated in the course of the use of the article by a user and consequently the effect of the anti-staining property is hardly maintained, that is, the hard coat layer is poor in anti-staining durability.
On the other hand, there is a method of improving the anti-staining property by incorporating an additive such as silicone oil or a fluoropolymer to the hard coat layer. However, these additives are the substances generally referred to as soft segment and have a property to impart flexibility to a resin, and hence the addition of these additives offers a drawback to degrade the mechanical strength of the hard coat layer such as the surface hardness as a function of the hard coat layer.
For example, Japanese Patent Laid-Open No. 2004-047040 (Patent Document 1) describes an optical recording medium characterized in that a coating layer made of an anti-staining agent is formed on the reading side surface on which incident is the laser light conducting at least recording or reproduction of the information signal (claim 1). However, the anti-staining agent described in Patent Document 1 includes an alkoxysilane compound having a perfluoro polyether group or a fluoroalkyl group, and is different from compositions for the hard coat layer according to the present invention.
Japanese Patent Laid-Open No. 2002-367229 (Patent Document 2) describes an optical information recording medium in which at least a reflective film, a recording film and a protective film are provided on one surface of the substrate of the optical information recording medium, and the protective film is formed as a surface layer on the one surface of the substrate, wherein a hard coat resin layer is formed as an outer layer of at least one selected from the substrate and the protective film, and a chemical adsorption film made of organic silane molecules is formed as an outer layer of the hard coat resin layer so as to be bonded to the hard coat layer through a covalent bond (claim 1). The hard coat layer of Patent Document 2 is, as described therein, a so-called double layered hard coat layer in which the chemical adsorption film formed by covalent bonds is further provided on the surface of the hard coat resin layer, and is significantly different in constitution from the hard coat layer of the present invention.
Japanese Patent Laid-Open No. 2006-107572 (Patent Document 3) describes a hard coat surface treatment method wherein a hard coat surface formed by curing an organic hard coat material containing an energy ray curable compound is subjected to a plasma treatment in an atmosphere into which introduced is a gas of a fluorinated hydrocarbon containing fluorine atoms in the molecule (claim 1). Patent Document 3 describes that according to this method, there is provided a hard coat surface treatment method in which the medium surface is imparted with water repellency and oil repellency by means of a low cost and simple process; however, this method requires a specific large scale apparatus in order to conduct the plasma treatment under a specific atmosphere, and hence is insufficient as a simple and low cost process.
Japanese Patent Laid-Open No. 2003-277478 (Patent Document 4) describes an epoxy resin composition that includes: an epoxy resin having in one molecule at least two cyclic aliphatic epoxy groups, at least one perfluoroalkyl group having 6 to 12 carbon atoms and at least one alkylsiloxane group; and a cationic polymerization catalyst, wherein the cyclic aliphatic epoxy group and the perfluoroalkyl group are present in the branched chains of the epoxy resin, and the alkylsiloxane group is present in the main chain of the epoxy resin (claim 1). Patent Document 4 is concerned with a composition that is applied to a liquid jet recording head, and the layer formed from the composition has anti-staining property, but is insufficient for a hard coat layer that also has the mechanical strength such as the surface hardness required in information recording media, various display elements or the like.
Japanese Patent Laid-Open No. 2005-206829 (Patent Document 5) describes a fluorine-containing curable coating liquid containing a fluorine-containing compound having a film formability and a polymerizable double bond, and a fluorine-containing (meth)acrylic acid ester having no film formability (claim 1). Similarly to Patent Document 4, the layer formed from the coating liquid of Patent Document 5 has anti-staining property, but is insufficient for a hard coat layer that also has the mechanical strength such as the surface hardness required in information recording media, various display elements or the like. As a technique to improve the surface hardness, it is possible to provide a hard coat layer and to form thereon a fluorine-containing curable coating film; however, this method suffers from a trouble that the fluorine-containing curable coating film is dissipated in the course of the use by a user to lead to poor anti-staining durability.
Japanese Patent Laid-Open No. 11-43648 (Patent Document 6) describes a curable resin composition for a coating material including: (a) a silicone-acrylic block copolymer obtained by polymerizing at least one kind of acrylic monomer having a cross-linkable functional group or a mixture composed of said acrylic monomer and another ethylenically unsaturated monomer in the presence of a silicone macro initiator that includes a plurality of polysiloxane chains having both terminals linked with a 2,2′-azobisnitrile group; (b) a film forming resin having a functional group capable of cross-linking with the same curing agent as for the cross-linkable functional group of the (a) component, or having a functional group that mutually reacts with the functional group of the (a) component; and (c) a curing agent that reacts at least with the (b) component (claim 1). However, the composition described in Patent Document 6 is different from the composition applied to the present invention, and is insufficient for the hard coat layer having anti-staining property, anti-staining durability, scratch resistance and abrasion resistance, without impairing the optical properties and the recording properties as required for articles and various display elements.
Japanese Patent Laid-Open No. 2002-363495 (Patent Document 7) describes a coating composition including: (a) a fluorine/silicone-acrylic block copolymer obtained by polymerizing a monomer mixture A including a fluorine-containing unsaturated monomer (a-1) and an acrylic monomer (a-2) having a reactive functional group, in the presence of a silicone macro initiator that includes a plurality of polysiloxane chains having both terminals linked with a 2,2′-azobisnitrile group; (b) a fluorine-containing copolymer obtained by polymerizing a monomer mixture B including a fluorine-containing unsaturated monomer (b-1) and an acrylic monomer (b-2) having a reactive functional group; and (c) a curing agent (claim 1). However, the composition described in Patent Document 7 is different from the composition applied to the present invention, and is insufficient for the hard coat layer having anti-staining property, anti-staining durability, scratch resistance and abrasion resistance, without impairing the optical properties and the recording properties as required for articles and various display elements.